#ESETresearch discovered and reported to @certcc 11 old Microsoft-signed UEFI shim bootloaders that allow bypassing UEFI Secure Boot on most UEFI systems. Read about it at https://www.welivesecurity.com/en/eset-research/forgotten-uefi-shims-undermining-secure-boot/ Tracked by #CVE-2026-8863 and #CVE-2026-10797, all these vulnerable shims were revoked in Microsoft’s June Patch Tuesday updates. https://www.cve.org/CVERecord?id=CVE-2026-8863 https://www.cve.org/CVERecord?id=CVE-2026-10797 Exploiting these vulnerable shims allows execution of untrusted code at system boot by using the Bring Your Own Vulnerable Driver (#BYOVD) technique, enabling deployment of malicious UEFI bootkits on systems that trust the Microsoft Corporation UEFI CA 2011 certificate. What makes these old shims dangerous is not a novel vulnerability, it’s that no new vulnerability is needed to bypass Secure Boot. Just an old, still-trusted, unrevoked shim and basic knowledge of how UEFI works is enough to bypass UEFI Secure Boot and deploy a UEFI bootkit. For more details and instructions on how to verify that the dbx patches were properly applied on your system, read our blogpost: https://www.welivesecurity.com/en/eset-research/forgotten-uefi-shims-undermining-secure-boot/